Recent information has shed new light on the importance of the V1/V2 domain of HIV-1 in viral infection and as a potential target for protective vaccines. The V1/V2 domain has been shown to be a critical determinant of an increasing number of monoclonal antibodies (mAbs) isolated from HIV-infected subjects that that target quaternary neutralization epitopes and possess broad and potently neutralizing activities. In addition to the role of the V1/V2 region as a classical neutralization target other evidence has accumulated showing that the interaction between a conserved V2 sequence and the 47-integrin receptor stimulates infection of a fraction of activated T cells in the gut that may be important for infection in vivo, and that this interaction is inhibited by anti-V2 mAbs. Finally, a analysis of immune parameters in the RV144 vaccine trial recently carried out in Thailand showed that antibodies that bind to a V1/V2 fusion protein that we developed uniquely correlated with protection. Studies from our lab and others have shown that potent V1/V2 neutralization targets are both highly conformational and glycan-dependent, and developing V1/V2-based vaccines is complicated by the structural heterogeneity of this region, due to variation in both protein folding and glycosylation. The aims of this project are to fully characterize the structural, functional and immunological properties of the V1/V2 domain, to identify and characterize protective epitopes in this region and to develop immunogens and vaccine strategies specific for conserved V1/V2 epitopes that efficiently elicit antibodies that contribute to protection against infection. The efficacy of novel V1/V2 immunogens developed by this program will be evaluated initially in a rabbit model by Dr. Shan Lu at UMass and towards the end of this study in a non-human primate challenge model by Dr. Shiu-Lok Hu at the WNPRC. The optimization of targets in the V1/V2 domain arising from these studies should be an important contribution towards the design of more effective HIV vaccines.